Question

I don’t really know how to explain except with “vertical where”.

Imagine the following table:

TAGID|PRODUCTID|SHOP_ID
59   |3418-7   |38
61   |3418-7   |38
60   |4227-4   |38
61   |4227-4   |38

Now I want to return all product IDs, that have relation to the tag IDs: 59,61. In other words, values of product ID where rows exist for both tag IDs.

So I want to return 3418-7, but not 4227-4

How do I write this as simple as possible in a SQL statement?

This is the working statement I have so far, but I feel this could be done in a much smarter way:

SELECT 
  productid 
FROM shop_tag_relations 
WHERE 
  productid IN (select productid from shop_tag_relations WHERE tagid=59) 
AND 
  productid IN (select productid from shop_tag_relations WHERE tagid=61)
GROUP BY productid,shop_id

Answer 1

SELECT PRODUCTID
FROM T
WHERE TAGID IN (59,61)
GROUP BY PRODUCTID
HAVING COUNT(DISTINCT TAGID) = 2

Or

SELECT PRODUCTID
FROM T
WHERE TAGID = 59
INTERSECT
SELECT PRODUCTID
FROM T
WHERE TAGID = 61